Storage media is used for storing recorded data. One example of a storage media used for magnetic recording is a disk. Two types of disks that are used for magnetic recording of data are discrete track media (DTM) type disk and bit patterned media (BPM) type disk. Patterns that are formed on a DTM disk or BPM disk are grooves and lands. A groove (e.g., depressions or pits) has a top surface which is below the height of the original disk surface. A land has a top surface which is typically at the same height as the original disk surface.
A disk will have servo zones in which servo data is recorded, and data zones which are the data recording region. The servo data is used for guiding and controlling the position of the read-write slider (i.e., head) which is used for reading from and writing to the disk. For example, the servo data will maintain the position of the head along the center of the data track in the data zones of the disk and guide the head from one data track to another data track.
In a DTM disk, a data zone includes a set of parallel and concentrically-arranged lands, and a land is separated by parallel and concentrically-arranged grooves. Each data zone is between servo zones. The lands in the data zones and servo zones store magnetically recorded information.
In a BPM disk, multiple “bit islands”, which may be lands in the shape of a square (or rectangles), are concentrically-arranged around the disk. The islands will store the magnetically recorded information in the form of bit values. The bit islands are separated by grooves in the disk and these grooves are non-magnetized areas that do not store information.
However, the topographic patterns (in the form of lands, grooves, or bit islands) on a disk will change the air flow between the slider and the disk. For example, in a DTM disk, the difference in the topographic pattern of a servo zone and the topographic pattern in a data zone will cause a change in the air flow under the slider as the slider is sequentially disposed from a data zone to a servo zone and vice versa. This change in air flow under the slider may cause the slider to move up and down (i.e., cause modulations in the slider flying height) when the disk moves under the slider. These slider flying height modulations typically will lead to magnetic spacing modulation which degrades the read and write performance of the slider, and also degrades the control of the slider because the slider is also trying to read the servo data.
Additionally, in a BPM disk, the bit islands can also vary in shape, positions, and number. These variations in the topography in a BPM disk can potentially lead to decreases and increases in the air flow that lead to slider flying height modulations.
Therefore, it is advantageous to reduce the modulations of the slider flying height and to reduce the air disturbances on the air bearing surface of the slider that flies over the disk.